Does a PoE injector need a separate power source?

Yes, a PoE injector requires a separate power source to function. While a PoE injector is used to send both power and data over the same Ethernet cable to a PoE-enabled device, it does not generate power on its own. Instead, it draws power from an external power supply to inject into the Ethernet cable alongside the data signal.

Here’s a detailed explanation of how it works and the specific power requirements:

1. Power Source for a PoE Injector

External Power Supply: A PoE injector typically comes with a power adapter or needs to be connected to an external AC power source. The power adapter is used to convert the AC power from your electrical outlet into DC power that the PoE injector can use to inject power into the Ethernet cable.

Power Ratings: The power supply needs to provide enough power to support both the PoE injector itself and the powered device (PD) that will receive power through the Ethernet cable. Different PoE standards (e.g., 802.3af, 802.3at, and 802.3bt) require different amounts of power:

--- 802.3af (PoE): Typically requires 15.4 watts of DC power.

--- 802.3at (PoE+): Typically requires 25.5 watts of DC power.

--- 802.3bt (PoE++ or 4PPoE): Can require up to 60 watts (Type 3) or even 100 watts (Type 4).

PoE Injector’s Power Supply: For a PoE injector to deliver power over Ethernet, it requires a power supply that provides the necessary wattage. The injector needs a higher power rating than the power it needs to deliver to the device because there will be power loss due to the efficiency of the power conversion process.

2. How the Power Supply Works

--- Power Input: The PoE injector is typically plugged into an AC power outlet using the provided power adapter or an external power supply unit (PSU).

--- The power is usually AC (alternating current), and it is converted into DC (direct current) by the adapter or PSU inside the injector.

--- Power Output: The injector then takes this DC power and injects it into the Ethernet cable along with the data signal, ensuring that the connected device (such as an IP camera, access point, or VoIP phone) receives both power and data over a single Ethernet cable.

--- Power Requirements for the Device: The power requirements of the device being powered over Ethernet determine how much power the injector needs to supply. For example:

--- A PoE-enabled IP camera may need 15.4W for standard PoE or up to 25.5W for PoE+.

--- A high-power access point or PTZ camera may require up to 60W or more, which requires a PoE injector that supports PoE++ (802.3bt Type 3 or 4).

3. Power Delivery Over Ethernet

--- Combined Power and Data Transmission: The key feature of a PoE injector is its ability to deliver both data and power over the same Ethernet cable. The injector essentially sends DC power to the powered device (PD) while the network switch or router sends data through the cable.

Power Budget: PoE injectors come with a power budget, which is the total amount of power the injector can provide across all PoE ports. The power budget is limited by the capacity of the power supply that powers the injector. For example:

--- A PoE injector with a 15W power supply can deliver up to 15.4W of power on each PoE port, assuming the cable quality is sufficient.

--- For higher power PoE injectors (e.g., supporting PoE+ or PoE++), a more powerful PSU will be needed to support multiple devices or high-power devices, as these require more power.

4. Connecting the Power Supply to the Injector

When setting up a PoE injector:

--- Power Source Connection: Plug the PoE injector’s power adapter into a standard AC power outlet.

--- Injector to Network: Use an Ethernet cable to connect the LAN/Data In Port on the PoE injector to your router or network switch.

--- Injector to PoE Device: Use another Ethernet cable to connect the PoE Out Port on the injector to your PoE-enabled device (such as an IP camera, VoIP phone, or access point).

--- The injector will deliver both data and power to the device through the Ethernet cable.

5. Types of PoE Injectors and Their Power Sources

--- Single-Port PoE Injector: Designed to supply power to a single PoE-enabled device. These typically require a wall-mounted AC adapter that plugs into the injector.

--- Multi-Port PoE Injector: These injectors can supply power to multiple PoE devices (e.g., 4, 8, 16 ports). They will require a larger external power supply to handle the increased power needs. For example, a 16-port PoE injector may require an external power supply of 250W or more to provide sufficient power across all ports.

--- High-Power PoE Injector (PoE++ or 802.3bt): These injectors are designed to deliver higher wattages (up to 100W per port). They require even higher power supplies, and the injector itself will be larger and may require a dedicated power cable or power brick for sufficient power delivery.

6. Conclusion

A PoE injector does need a separate power source in the form of an AC-to-DC adapter or an external power supply.

--- The injector requires this power source to inject power (along with data) into the Ethernet cable to the powered device.

--- The power supply must provide sufficient wattage to handle both the injector itself and the devices it powers. The exact wattage depends on the PoE standard (802.3af, 802.3at, 802.3bt) and the number of devices being powered.

By providing the necessary power and maintaining stable data communication, PoE injectors are a practical solution for powering and connecting network devices, especially in locations where power outlets are not available or feasible.